South-west wastewater upgrade

Project overview

As the south-west of Auckland develops we need to expand our wastewater treatment infrastructure to support population growth in Waiuku, Glenbrook Beach, Clarks Beach and Kingseat. The treatment plants currently serving these communities are coming to the end of their operational life and the area is growing. We are developing a long-term solution that will support growth through to 2050. We are committed to improving the Manukau Harbour and to do this we will be using state of the art technology to significantly advance the quality of treated wastewater. Some of this technology is currently being installed at Clarks Beach where we are delivering an upgrade project while we wait for a long-term solution to be delivered.

History

Our plan had previously been to replace these plants with one larger facility that can meet the needs of 30,000 people. In 2023, we purchased land in Glenbrook and lodged a Notice of Requirement with Auckland Council to designate it for wastewater treatment purposes. Council referred it to a panel of independent commissioners for assessment under the Resource Management Act 1991.

In late May 2024, the panel of independent commissioners recommended we withdraw our Notice of Requirement. After reviewing the commissioners’ feedback, we decided not to pursue the designation of our land in Glenbrook for wastewater treatment purposes.

Our decision-making process

We have been reassessing options to find a sustainable, affordable and appropriate long-term solution that can deliver environmental benefits while allowing for growth.

The options assessed included using our existing wastewater treatment plant sites at Waiuku and Clarks Beach, a new treatment plant on one of two new sites on NZ Steel owned land at Waiuku, or a new plant at our previously preferred site at 372 Glenbrook Beach Road.

A longlist of eight options was developed, across five possible sites. In February 2025, we held drop-in sessions in Waiuku, Clarks Beach and Glenbrook Beach to discuss this longlist with the community.

The options were then evaluated using a multi-criteria analysis (MCA) that looked at the pros and cons of each option against a wide range of criteria.

In March 2025, we held community drop-in session to talk about the short list of options before revisiting the MCA. We returned to present our preferred wastewater servicing solution in July.

What is our preferred wastewater servicing solution?

The preferred solution is a decentralised scheme utilising our existing Clarks Beach and Waiuku sites that will service up to 30,000 people. This will include:

• New, upgraded wastewater treatment plants (WWTPs) on our existing sites at Waiuku and Clarks Beach.

• A new pipeline to carry treated wastewater from Waiuku to Clarks Beach.

• An interim upgrade of our existing plant at Waiuku to meet existing consent conditions while we undertake the main upgrade.

• Tidal storage on our Waiuku and Clarks Beach WWTP sites.

This option will provide capacity for up to 30,000 people, and based on Auckland Council’s current population growth projections, will support growth to at least 2050.

Beyond this, we have the option of transitioning to a centralised wastewater treatment plant at our Waiuku site. This would involve constructing a new pipeline to carry untreated wastewater from Clarks Beach to Waiuku, expand the Waiuku WWTP site and decommission most of the Clarks Beach WWTP site. This option was the best scoring long term option under the MCA.

We are unable to provide an exact date for transitioning to a centralised plant at Waiuku as it will be dependent on population growth.

Why was this option chosen?

It reflects the feedback we received from the community, and the independent commissioners, about our previously preferred option and the matters we should be considering. This staged plan also uses the existing system better, gives us more flexibility and costs less upfront.

How long will implementation take?

The exact timing for the work depends on receiving landowner approvals and the relevant consents. We will now look to close out the feasibility stage and undertake the design and consenting for the construction work. Once the design is complete, the main work will be tendered, and construction is expected to take approximately three years.